In current limiting switching devices of the above-mentioned kind, it is desirable that the arc leaves the contact material as quickly as possible and travels out on runner rails, which may, for example, be diverging to achieve a high arcing voltage, or which are adapted to insert a resistance into the circuit in order to limit the current.
In prior art switching devices operating in accordance with the above-mentioned principle, the arc commutation from the contacts to the runner rails has not taken place until a relatively large contact distance has been achieved and a relatively great amount of ionized gas has been formed at the front end of the runner rails. This deteriorates the current limiting ability of these devices.
In circuit breakers with separate main and break contacts it is known to arrange the movable break contact on a runner rail, which in turn is movably arranged in relation to the movable main contact (see e.g. German patent publication No. 1 272 423). In such a circuit breaker, a certain amount of time is required, on the one hand, for the current commutation from the main to the break contacts and, on the other hand, for the above-mentioned arc commutation from the break contacts to the runner rails.